1. Field of the Invention
The invention generally relates to automatic transmissions of motor vehicles, and in particular to an automatic transmission which includes a plurality of planetary gear sets and provides seven or more forward gear stages, and which has a relatively small size and operates with a reduced loss.
2. Description of Related Art
Automatic transmissions of motor vehicles each having a plurality of planetary gear sets, clutches and brakes have been widely used. One example of such automatic transmissions as disclosed in Japanese Laid-open Patent Publication No. 2000-266138 is able to provide seven forward gear stages by using four planetary gear sets.
However, the use of the four planetary gear sets in the known automatic transmission causes an increase in the axial length of the transmission and an increased difficulty in installing the transmission on the vehicle, and also results in increases in the weight and cost of the transmission. Furthermore, the known automatic transmission includes seven friction devices which are selectively engaged and released for establishing seven gear stages. Thus, the known transmission requires an increased number of components, which results in an increased cost, and suffers from relatively large drag resistance, which causes deterioration in the fuel economy.
It is therefore an object of the invention to provide an automatic transmission of a motor vehicle which is able to provide seven or more forward gear stages or speeds by using three or four planetary gear sets and a reduced number of friction devices.
To accomplish the above object, there is provided according to a first aspect of the invention an automatic transmission, which comprises (a) an input member, (b) an output member, (c) an auxiliary power transmitting portion including a planetary gear set having three rotating elements, wherein when one of the three rotating elements is coupled to and rotated with the input member and another one of the rotating elements is fixed to be inhibited from rotating, the remaining rotating element serving as an intermediate rotating element is rotated at a reduced speed as compared with that of the input member, the auxiliary power transmitting portion further including an intermediate rotation output friction device that is operable, when engaged, to permit the intermediate rotating element to output rotary power at the reduced speed, and (d) a main power transmitting portion including a plurality of planetary gear sets including sun gears, carriers and ring gears, parts of which are coupled to each other to provide a first rotating element, a second rotating element, a third rotating element, a fourth rotating element and a fifth rotating element, which are arranged in the order of description from one end to the other end in a nomogram in which speeds of rotation of the first, second, third, fourth and fifth rotating elements are represented by straight lines, the main power transmitting portion further including a first brake, a second brake, a first clutch and a second clutch, wherein the first rotating element is coupled to the intermediate rotating member and is selectively inhibited from rotating by the second brake, the second rotating element is selectively inhibited from rotating by the first brake, the third rotating element is selectively coupled to the input member via the second clutch, the fifth rotating element is selectively coupled to the input member via the first clutch, and the fourth rotating element is coupled to the output member so as to output rotary power from the main power transmitting portion. In this automatic transmission, a first-speed gear stage having the largest gear ratio is established when the first clutch and the first brake are engaged, a second-speed gear stage having a smaller gear ratio than that of the first-speed gear stage is established when the first clutch and the second brake are engaged, a third-speed gear stage having a smaller gear ratio than that of the second-speed gear stage is established when the first clutch and the intermediate rotation output friction device are engaged, a fourth-speed gear stage having a smaller gear ratio than that of the third-speed gear stage is established when the first clutch and the second clutch are engaged, a fifth-speed gear stage having a smaller gear ratio than that of the fourth-speed gear stage is established when the second clutch and the intermediate rotation output friction device are engaged, a sixth-speed gear stage having a smaller gear ratio than that of the fifth-speed gear stage is established when the second clutch and the second brake are engaged, and a seventh-speed gear stage having a smaller gear ratio than that of the sixth-speed gear stage is established when the second clutch and the first brake are engaged.
The automatic transmission constructed as described above is able to establish seven forward gear stages by using three planetary gear sets and a total of five friction devices. Thus, the weight and size of the transmission can be reduced as compared with the case where four planetary gear sets are used. At the same time, the number of friction devices required for shifting the transmission is reduced, resulting in a reduced number of components and reduced cost. Furthermore, the drag resistance is reduced, and the fuel economy can be further improved.
According to a second aspect of the invention, there is provided an automatic transmission, which comprises (a) an input member, (b) an output member, (c) an auxiliary power transmitting portion including a planetary gear set having three rotating elements, wherein when one of the three rotating elements is coupled to and rotated with the input member, and another one of the rotating elements is fixed to be inhibited from rotating, the remaining rotating element serving as an intermediate rotating element is rotated at a reduced speed as compared with that of the input member, the auxiliary power transmitting portion further including an intermediate rotation output friction device that is operable, when engaged, to permit the intermediate rotating element to output rotary power at the reduced speed, and (d) a main power transmitting portion including a plurality of planetary gear sets including sun gears, carriers and ring gears, parts of which are coupled to each other to provide a first rotating element, a second rotating element, a third rotating element, a fourth rotating element and a fifth rotating element, which are arranged in the order of description from one end to the other end in a nomogram in which speeds of rotation of the first, second, third, fourth and fifth rotating elements are represented by straight lines, the main power transmitting portion further including a first brake, a second brake, a first clutch and a second clutch, wherein the first rotating element is selectively coupled to the input member via the second clutch and is selectively inhibited from rotating by the second brake, the second rotating element is selectively inhibited from rotating by the first brake, the third rotating element is selectively coupled to the input member via the first clutch, the fifth rotating element is coupled to or selectively coupled to the intermediate output member, and the fourth rotating element is coupled to the output member so as to output rotary power from the main power transmitting portion. In this automatic transmission, a first-speed gear stage having the largest gear ratio is established when the intermediate rotation output friction device and the first brake are engaged, a second-speed gear stage having a smaller gear ratio than that of the first-speed gear stage is established when the intermediate rotation output friction device and the second brake are engaged, a third-speed gear stage having a smaller gear ratio than that of the second-speed gear stage is established when the second clutch and the intermediate rotation output friction device are engaged, a fourth-speed gear stage having a smaller gear ratio than that of the third-speed gear stage is established when the first clutch and the intermediate rotation output friction device are engaged, a fifth-speed gear stage having a smaller gear ratio than that of the fourth-speed gear stage is established when the first clutch and the second clutch are engaged, a sixth-speed gear stage having a smaller gear ratio than that of the fifth-speed gear stage is established when the first clutch and the second brake are engaged, and a seventh-speed gear stage having a smaller gear ratio than that of the sixth-speed gear stage is established when the first clutch and the first brake are engaged.
The automatic transmission constructed as described above is able to establish seven forward gear stages by using three or four planetary gear sets and a total of five friction devices. Thus, the weight and size of the transmission can be reduced as compared with the case where four planetary gear sets and a total of seven friction devices are used. At the same time, the number of friction devices required for shifting the transmission is reduced, resulting in a reduced number of components and reduced cost. Furthermore, the drag resistance is reduced, and the fuel economy can be further improved.
According to a third aspect of the invention, there is provided an automatic transmission, which comprises (a) an input member, (b) an output member, (c) an auxiliary power transmitting portion including a planetary gear set having three rotating elements, wherein when one of the rotating elements is coupled to and rotated with the input member, and another one of the rotating element is fixed to be inhibited from rotating, the remaining rotating element serving as an intermediate rotating element is rotated at a reduced speed as compared with that of the input member, the auxiliary power transmitting portion further including an intermediate rotation output friction device that is operable, when engaged, to permit the intermediate rotating element to output rotary power at the reduced speed, and (d) a main power transmitting portion including a plurality of planetary gear sets including sun gears, carriers and ring gears, parts of which are coupled to each other to provide a first rotating element, a second rotating element, a third rotating element, a fourth rotating element and a fifth rotating element, which are arranged in the order of description from one end to the other end in a nomogram in which speeds of rotation of the first, second, third, fourth and fifth rotating elements are represented by straight lines, the main power transmitting portion further including a first brake, a second brake, a first clutch, a second clutch and a third clutch, wherein the first rotating element is selectively inhibited from rotating by the second brake and is selectively coupled to the intermediate rotating member via the third clutch, the second rotating element is selectively inhibited from rotating by the first brake, the third rotating element is selectively coupled to the input member via the second clutch, the fifth rotating element is selectively coupled to the intermediate rotating member via the first clutch, and the fourth rotating element is coupled to the output member so as to output rotary power from the main power transmitting portion. In this automatic transmission, a first-speed gear stage having the largest gear ratio is established when the first clutch and the first brake are engaged, a second-speed gear stage having a smaller gear ratio than that of the first-speed gear stage is established when the first clutch and the second brake are engaged, a third-speed gear stage having a smaller gear ratio than that of the second-speed gear stage is established when the first clutch and the third clutch are engaged, a fourth-speed gear stage having a smaller gear ratio than that of the third-speed gear stage is established when the first clutch and the second clutch are engaged, a fifth-speed gear stage having a smaller gear ratio than that of the fourth-speed gear stage is established when the second clutch and the third clutch are engaged, a sixth-speed gear stage having a smaller gear ratio than that of the fifth-speed gear stage is established when the second clutch and the second brake are engaged, and a seventh-speed gear stage having a smaller gear ratio than that of the sixth-speed gear stage is established when the second clutch and the first brake are engaged.
The automatic transmission constructed as described above is able to establish seven or more forward gear stages by using three planetary gear sets and a total of five friction devices, i.e., three clutches and two brakes. Thus, the weight and size of the transmission can be reduced as compared with the case where four planetary gear sets are used. At the same time, the number of friction devices required for shifting the transmission is reduced, resulting in a reduced number of components and reduced cost. Furthermore, the drag resistance is reduced, and the fuel economy can be further improved.